> I would move this if in here, so that we always send an observer notification.  ...

?!
The `nttAddonCompatibilityService` sends the notification in __all case__. See the other, `sendNotification()`, `notifyObject` related threads near at line `L54` and `L73`/`L83`!

The `restartObserver` here isn't always activated. 
For example Songbird doesn't have `nightlyApp.openNotification` implemented yet,
therefore `nightly.toggleCompatibility` doesn't register for the restart notification.
It simply discards. :)
But in Firefox case it will register the observer, and the PopupNotification/NotificationBox could open if restart would be needed after pref change.